Abstract: Based on theprehensive analysis on the plastic partstructure service requirement moundingintroduced记叙文记叙文开头句子的作用:开篇点题总领全文引起下文为下文作铺垫设置悬念引起读者的兴趣或思考记叙文中间句子的作用:单独成段起承上启下的过渡作用段末起总结作用(总结上文引